Japanese black pine seedling problem

[sarcpilot]

Hi, I have 2 japenese black pine seedlings about 1.5 years old now, and some of the needles is turning dark and brown. (the 2 pics thats attached is of both the trees), they stay outside, full sun. The soil that they are in now is a akadama and crushed silica mix. I stay in South Africa it's the start of autumn now. I give them fertilizer every 2 weeks during the growing season and only water when the soil starts to dry out. Anyone know what can cause this?

 

[Paradox]

Looks like it could be a fungus. Banding on the needles is most likely needle cast.

Unfortunately with needle cast, you need to treat preventatively for because it infects the needles the year before you see any evidence of it.

Is the area you in pretty humid?
Also please put your location on your profile
A lot of bonsai information and advice is location dependant. It helps us to know where you are to give the best advice without having to ask every time.

 

[sarcpilot]

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[sarcpilot]

Thank you

It's not humid where I stay, I also get a winter rain fall.

I'll try to put my location on my profile

 

[River's Edge]

Does not look like needle cast to me, looks more like the seedlings are drying out or affected by the strength of fertilizer being used! the mix looks like it drains very well so I would be inclined to increase the watering and be sure to water thoroughly. Water until it is draining freely out the bottom and running clear. This ensure the flushing of extra salts and provides fresh air and moisture levels in the pot. Seedlings that size do not have extensive root systems and require more frequent watering than established saplings for example. If you are not doing so use a 1/2 strength dose of fertilizer and switch to once every two or three weeks to see if that makes an improvement as well. These are general suggestions without the benefit of understanding your specific care routines. The other aspect could be a very windy/dry location which would speed the drying and would be improved by the two modifications suggested above.

 

[Shibui]

Agree with @River's Edge
Internet talk of pines having problems with overwatering has many new growers scared to water so trees dehydrate. Silica/akadama mix probably does not hold much water so may be prone to getting drier than anticipated. Problem appearing after summer is probably related.

Please consider the possibility the trees have dried out a bit too much, even occasionally. Symptoms don't usually appear for weeks after the event so we've often forgotten about the long weekend when we forgot to water, etc.

 

[sarcpilot]

Thanks @River's Edge and @Shibui

I now notice that the one is getting worse and one of the other is also showing similar symptoms

There was a time in summer that they got quite dry tho

 

[sarcpilot]

So I waited a while, I believe that this is needle cast, it started to make yellow spots on the needles and some dark bands around the needle...

 

[Paradox]

So I waited a while, I believe that this is needle cast, it started to make yellow spots on the needles and some dark bands around the needle...

Can you post a current picture?

Please put your location on your profile so we can give you the best advice based on your location if relevant. Just the city and state you are in is fine, we don't want your actual address. Your location information tells us something about your annual climate and weather cycle and can be very important for giving you the correct advice.

 

[sarcpilot]

Can you post a current picture?

Please put your location on your profile so we can give you the best advice based on your location if relevant. Just the city and state you are in is fine, we don't want your actual address. Your location information tells us something about your annual climate and weather cycle and can be very important for giving you the correct advice.

Sorry for only replying now

Will put my location on my profile

 

[sarcpilot]

Can you post a current picture?

Please put your location on your profile so we can give you the best advice based on your location if relevant. Just the city and state you are in is fine, we don't want your actual address. Your location information tells us something about your annual climate and weather cycle and can be very important for giving you the correct advice.

Here is another one, do you also think it's needle cast if so how whould you treat it?

 

[Shibui]

The horizontal bands around the needles look suspiciously like Dothostroma AKA needle cast. Not so sure about all the older brown needles though.
Treating for needle cast won't hurt even if it's not the correct diagnosis. I'm pretty sure any leaf fungicide stops it. Not sure what's available in SA but Copper sprays are normally recommended and should be readily available.
You'll need a minimum of 2 sprays each year. One at the start of spring protects last year's needles and a follow up when the new needles have opened fully in early summer. Normally, summer sprays are not required but if you are watering the needles through summer you'd be advised to spray a couple more times through the warm months.

Note that you cannot cure needles that are already damaged. The best you can hope for is to stop further infection of the new needles next season.

 

[Paradox]

As shuibui stated, you can't cure the current infected needles. This is because the needles are actually infected one year before its visible on the needle so by that time, it's too late. So we need to spray fungicide as a preventative.

If you are in an area prone to fungus or as said above, the needles are wet often, I'd spray once a month from spring to early fall. It is a good idea to rotate between two kinds of fungicide each month if you can.